1. Field of the Invention
The present invention relates, generally to a method of determining when a vehicle seat has become unoccupied and, more specifically, to a method of early prediction of an empty seat condition for a vehicle seat having an occupancy sensing system.
2. Description of the Related Art
Automotive vehicles employ seating systems that accommodate the passengers of the vehicle. The seating systems include restraint systems that are calculated to restrain and protect the occupants in the event of a collision. The primary restraint system commonly employed in most vehicles today is the seatbelt. Seatbelts usually include a lap belt and a shoulder belt that extends diagonally across the occupant's torso from one end of the lap belt to a mounting structure located proximate to the occupant's opposite shoulder.
In addition, automotive vehicles may include supplemental restraint systems. The most common supplemental restraint system employed in automotive vehicles today is the inflatable airbag. In the event of a collision, the airbags are deployed as an additional means of restraining and protecting the occupants of the vehicle. Originally, the supplemental inflatable restraints (airbags) were deployed in the event of a collision whether or not any given seat was occupied. These supplemental inflatable restraints and their associated deployment systems are expensive and over time this deployment strategy was deemed not to be cost effective. Thus, there became a recognized need in the art for a means to selectively control the deployment of the airbags such that deployment occurs only when the seat is occupied.
Partially in response to this need, vehicle safety systems have been proposed that include vehicle occupant sensing systems capable of detecting whether or not a given seat is occupied. The systems act as a switch in controlling the deployment of a corresponding air bag. As such, if the occupant sensing device detects that a seat is unoccupied during a collision, it can prevent the corresponding air bag from deploying, thereby saving the vehicle owner the unnecessary cost of replacing the expended air bag.
Furthermore, many airbag deployment forces and speeds have generally been optimized to restrain one hundred eighty pound males because the one hundred eighty pound male represents the mean average for all types of vehicle occupants. However, the airbag deployment force and speed required to restrain a one hundred eighty pound male exceeds that which are required to restrain smaller occupants, such as some females and small children. Thus, there became a recognized need in the art for occupant sensing systems that could be used to selectively control the deployment of the airbags when a person below a predetermined weight occupies the seat.
Accordingly, other vehicle safety systems have been proposed that are capable of detecting the weight of an occupant. In one such air bag system, if the occupant's weight falls below a predetermined level, then the system can suppress the inflation of the air bag or will prevent the air bag from deploying at all. This reduces the risk of injury that the inflating air bag could otherwise cause to the smaller-sized occupant.
Also, many airbag deployment forces and speeds have generally been optimized to restrain a person sitting generally upright towards the back of the seat. However, the airbag deployment force and speed may inappropriately restrain a person sitting otherwise. Thus, there became a recognized need in the art for a way to selectively control the deployment of an airbag depending on the occupant's sitting position.
Partially in response to this need, other vehicle safety systems have been proposed that are capable of detecting the position of an occupant within a seat. For example, if the system detects that the occupant is positioned toward the front of the seat, the system will suppress the inflation of the air bag or will prevent the air bag from deploying at all. This reduces the risk of injury that the inflating air bag could otherwise cause to the occupant. It can be appreciated that these occupant sensing systems provide valuable data, allowing the vehicle safety systems to function more effectively to reduce injuries to vehicle occupants.
One necessary component of each of the known systems discussed above includes some means for sensing the presence of the vehicle occupant in the seat. One such means may include a sensor device supported within the lower seat cushion of the vehicle seat. For example, U.S. published patent application having U.S. Ser. No. 10/249,527 and Publication No. US2003/0196495 A1 filed in the name of Saunders et al. discloses a method and apparatus for sensing seat occupancy including a sensor/emitter pair that is supported within a preassembled one-piece cylinder-shaped housing. The housing is adapted to be mounted within a hole formed in the seat cushion and extending from the B-surface toward the A-surface of the seat cushion. The sensor/emitter pair supported in the housing includes an emitter that is mounted within the seat cushion and spaced below the upper or A-surface of the seat cushion. In addition, the sensor is also supported by the housing within the seat cushion but spaced below the emitter. The cylindrical housing is formed of a compressible, rubber-like material that is responsive to loads placed on the upper surface of the seat cushion. The housing compresses in response to a load on the seat cushion. The load is detected through movement of the emitter toward the sensor as the housing is compressed. The housing is sufficiently resilient to restore the emitter to full height when no load is applied to the upper surface of the seat cushion. The Saunders et al. system also includes a processor for receiving the sensor signals and interpreting the signals to produce an output to indicate the presence of an occupant in the seat.
Generally speaking, to perform pattern recognition and classification of a physical presence that occupies a vehicle seat, the sensors are arranged into a grid, or an array so that the sensors are collectively used to provide the raw input data as a depression pattern. In this manner, systems of the type known in the related art take the data taken from the sensor array and process it, by a number of different means, in an attempt to determine the physical presence in the seat. The means used by the prior art methods vary from the use of simple computational methods to sophisticated, artificial neural networks. However, regardless of the types of sensors or the types of data processing employed, in each of these prior art vehicle seating occupancy sensing systems the sensor array or gird is integrated into the lower seat assembly as it is constructed.
The weight of an occupant sitting the vehicle seat causes the lower seat cushion to be compressed, which in turn causes a deflection of the sensors located in the sensor array. If the components of the seat are properly constructed in relation to each other, the compression of the cushion will adequately deflect the sensors to provide a good representative pattern of the occupant to the occupancy sensing system. It is important to note that, given this manner of seat construction, the occupancy sensing system must rely to some extent on the physical properties of the material used for the cushion. For example, foam materials are commonly employed in lower seat cushions and vary greatly, depending on their composition and intended application. When employed as seat cushioning materials, the foam cushion of the vehicle seat has certain physical properties and characteristics that can influence how the foam cushion deflects the sensors of the sensor array. By their nature, the foam materials used in seat cushions maintain a “memory” of their original shape and attempt to return to that shape after the force exerted by an occupant has been removed. The foam's ability to return to its original shape is a function of the foam's firmness and is referred to as the “hysteresis” of the foam. More specifically, the hysteresis of the foam is its relative delay in recovering its original shape.
Generally speaking, the hysteresis of the foam will increase the longer the foam has been deformed and the greater the deformation that was placed on the foam. This becomes important to occupancy sensing systems as an occupant leaves the seat and the vehicle remains in operation. For example, this situation may arise where a large male has occupied a seat for an extended period of time, such as a long trip. During this period, the seat foam has been substantially deformed as it responds to the passenger weight. Where the occupant exits the vehicle but the vehicle continues its trip, the sensor deflection caused by the slowly recovering foam seat cushion may cause the occupancy sensor system to falsely interpret the sensor readings as indicative of another occupant.
More specifically, in such an example, it will take a significant amount of time for the seat foam to overcome its hysteresis and completely return to it original shape. Typically, due to the resiliency and density of the foam cushioning materials commonly used, an exponential recovery of the foam will occur. Initially, a large portion of the foam recovery will occur rapidly with a continued but slower recovery to the original shape. Thus, even though the sensor array may be responsive to the departure of the individual, the sensors remain partially deflected due to the hysteresis and slow recovery of foam seat cushion.
This is problematic if an accident were to occur during the foam recovery period. If the vehicle is in an impact before the foam has time to completely recover from its hysteresis such that the occupant sensing system is unable to detect the empty seat, the supplemental restraint system would deploy the airbag on the empty seat. Additionally, it is possible that a much lighter adult or child could sit in the passenger seat after the large male exits. This means that the airbag could be allowed to improperly deploy against a small individual for whom it is actually desired to suppress or limit the airbag deployment. This would precipitate the same situation and possible injurious results that the occupancy sensing systems are attempting to prevent.
These issues relating to foam hysteresis are generally not a problem when an individual of a weight approximate to or heavier than the first individual takes the seat immediately after the first exits the vehicle. This second individual of the same or heavier weight would merely cause the foam to stay at the same deflection or cause deeper foam compression. However, if a lighter person occupies the seat immediately following a larger one, the recovery of the foam to the lighter individual's weight may be further delayed. Thus, even though the sensor array may be responsive to the departure of a first larger individual, the sensors remain temporarily deflected beyond the weight deflection of a second lighter individual due to the hysteresis and slow recovery of foam seat cushion.
Accordingly, there remains a need in the art for a method of predicting an empty vehicle seat for an occupancy sensing system, such that even with the hysteresis of the foam seat cushion deflecting the sensor array, the occupancy sensing system is aware that the seat is empty. Additionally, this need extends to not only predicting an empty seat condition but to determining the change in seat occupancy from a larger individual to a smaller one when applicable.